Isner guides U.S. to Davis Cup quarters

The big-serving American withstood a late Tomic rally to win 6-4, 6-4, 5-7, 7-6 (7-4) and give his team an unassailable 3-1 lead in Melbourne. The fifth rubber between Australia's Sam Groth and Jack Sock was not played.

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John Isner continued hurling down aces to help U.S. enter the Davis Cup quarterfinals on Sunday

John Isner overpowered Bernard Tomic in four sets as the United States booked its spot in the Davis Cup World Group quarterfinals on Sunday.

Big-serving American Isner withstood a late Tomic rally to win 6-4, 6-4, 5-7, 7-6 (7-4) and give his team an unassailable 3-1 lead in Melbourne, with the fifth rubber between Sam Groth and Jack Sock not played.

Isner, who saw off Groth in the opening singles match on Friday, was a class above right from the start as top-ranked Australian Tomic looked out of touch and out of sorts at Kooyong. Tomic had been hampered by a wrist problem heading into the first-round tie and Isner took advantage of his lethargic opponent.

Isner was eventually pegged back by Tomic, who emerged with renewed energy and focus to force a fourth set after the former saved four set points. However, that was as good as it got for Tomic as Isner prevailed in a tie-break, closing out the match with a service winner and ace — his 49th of the clash, without double-faulting.

The U.S. will now meet either Croatia or Belgium in the quarters, while Australia faces a World Group play-off in September.